Inbred corn line LH225

ABSTRACT

An inbred corn line, designated LH225, is disclosed. The invention relates to the seeds of inbred corn line LH225, to the plants of inbred corn line LH225 and to methods for producing a corn plant produced by crossing the inbred line LH225 with itself or another corn line. The invention further relates to hybrid corn seeds and plants produced by crossing the inbred line LH225 with another corn line.

This application is a continuation of application Ser. No. 08/140,371,filed Oct. 21, 1993, now U.S. Pat. No. 5,416,255.

BACKGROUND OF THE INVENTION

The present invention relates to a new and distinctive corn inbred line,designated LH225. There are numerous steps in the development of anynovel, desirable plant germplasm. Plant breeding begins with theanalysis and definition of problems and weaknesses of the currentgermplasm, the establishment of program goals, and the definition ofspecific breeding objectives. The next step is selection of germplasmthat possess the traits to meet the program goals. The goal is tocombine in a single variety or hybrid an improved combination ofdesirable traits from the parental germplasm. These important traits mayinclude higher yield, resistance to diseases and insects, better stalksand roots, tolerance to drought and heat, and better agronomic quality.

Choice of breeding or selection methods depends on the mode of plantreproduction, the heritability of the trait(s) being improved, and thetype of cultivar used commercially (e.g., F₁ hybrid cultivar, purelinecultivar, etc.). For highly heritable traits, a choice of superiorindividual plants evaluated at a single location will be effective,whereas for traits with low heritability, selection should be based onmean values obtained from replicated evaluations of families of relatedplants. Popular selection methods commonly include pedigree selection,modified pedigree selection, mass selection, and recurrent selection.

The complexity of inheritance influences choice of the breeding method.Backcross breeding is used to transfer one or a few favorable genes fora highly heritable trait into a desirable cultivar. This approach hasbeen used extensively for breeding disease-resistant cultivars. Variousrecurrent selection techniques are used to improve quantitativelyinherited traits controlled by numerous genes. The use of recurrentselection in self-pollinating crops depends on the ease of pollination,the frequency of successful hybrids from each pollination, and thenumber of hybrid offspring from each successful cross.

Each breeding program should include a periodic, objective evaluation ofthe efficiency of the breeding procedure. Evaluation criteria varydepending on the goal and objectives, but should include gain fromselection per year based on comparisons to an appropriate standard,overall value of the advanced breeding lines, and number of successfulcultivars produced per unit of input (e.g., per year, per dollarexpended, etc.).

Promising advanced breeding lines are thoroughly tested and compared toappropriate standards in environments representative of the commercialtarget area(s) for three years at least. The best lines are candidatesfor new commercial cultivars; those still deficient in a few traits areused as parents to produce new populations for further selection.

These processes, which lead to the final step of marketing anddistribution, usually take from eight to 12 years from the time thefirst cross is made. Therefore, development of new cultivars is atime-consuming process that requires precise forward planning, efficientuse of resources, and a minimum of changes in direction.

A most difficult task is the identification of individuals that aregenetically superior, because for most traits the true genotypic valueis masked by other confounding plant traits or environmental factors.One method of identifying a superior plant is to observe its performancerelative to other experimental plants and to a widely grown standardcultivar. If a single observation is inconclusive, replicatedobservations provide a better estimate of its genetic worth.

The goal of plant breeding is to develop new, unique and superior corninbred lines and hybrids. The breeder initially selects and crosses twoor more parental lines, followed by repeated selfing and selection,producing many new genetic combinations. The breeder can theoreticallygenerate billions of different genetic combinations via crossing,selfing and mutations. The breeder has no direct control at the cellularlevel. Therefore, two breeders will never develop the same line, or evenvery similar lines, having the same corn traits.

Each year, the plant breeder selects the germplasm to advance to thenext generation. This germplasm is grown under unique and differentgeographical, climatic and soil conditions, and further selections arethen made, during and at the end of the growing season. The inbred lineswhich are developed are unpredictable. This unpredictability is becausethe breeder's selection occurs in unique environments, with no controlat the DNA level (using conventional breeding procedures), and withmillions of different possible genetic combinations being generated. Abreeder of ordinary skill in the art cannot predict the final resultinglines he develops, except possibly in a very gross and general fashion.The same breeder cannot produce the same line twice by using the exactsame original parents and the same selection techniques. Thisunpredictability results in the expenditure of large research monies todevelop a superior new corn inbred line.

The development of commercial corn hybrids requires the development ofhomozygous inbred lines, the crossing of these lines, and the evaluationof the crosses. Pedigree breeding and recurrent selection breedingmethods are used to develop inbred lines from breeding populations,Breeding programs combine desirable traits from two or more inbred linesor various broad-based sources into breeding pools from which inbredlines are developed by selfing and selection of desired phenotypes. Thenew inbreds are crossed with other inbred lines and the hybrids fromthese crosses are evaluated to determine which have commercialpotential.

Pedigree breeding is used commonly for the improvement ofself-pollinating crops or inbred lines of cross-pollinating crops. Twoparents which possess favorable, complementary traits are crossed toproduce an F₁. An F₂ population is produced by selfing one or several F₁'s or by intercrossing two F₁ 's (sib mating). Selection of the bestindividuals is usually begun in the F₂ population; then, beginning inthe F₃, the best individuals in the best families are selected.Replicated testing of families, or hybrid combinations involvingindividuals of these families, often follows in the F₄ generation toimprove the effectiveness of selection for traits with low heritability.At an advanced stage of inbreeding (i.e., F₆ and F₇), the best lines ormixtures of phenotypically similar lines are tested for potentialrelease as new cultivars.

Mass and recurrent selections can be used to improve populations ofeither self- or cross-pollinating crops. A genetically variablepopulation of heterozygous individuals is either identified or createdby intercrossing several different parents. The best plants are selectedbased on individual superiority, outstanding progeny, or excellentcombining ability. The selected plants are intercrossed to produce a newpopulation in which further cycles of selection are continued.

Backcross breeding has been used to transfer genes for a simplyinherited, highly heritable trait into a desirable homozygous cultivaror inbred line which is the recurrent parent. The source of the trait tobe transferred is called the donor parent. The resulting plant isexpected to have the attributes of the recurrent parent (e.g., cultivar)and the desirable trait transferred from the donor parent. After theinitial cross, individuals possessing the phenotype of the donor parentare selected and repeatedly crossed (backcrossed) to the recurrentparent. The resulting plant is expected to have the attributes of therecurrent parent (e.g., cultivar) and the desirable trait transferredfrom the donor parent.

Descriptions of other breeding methods that are commonly used fordifferent traits and crops can be found in one of several referencebooks (e.g., Allard, 1960; Simmonds, 1979; Sneep et at., 1979; Fehr,1987).

Proper testing should detect any major faults and establish the level ofsuperiority or improvement over current cultivars. In addition toshowing superior performance, there must be a demand for a new cultivarthat is compatible with industry standards or which creates a newmarket. The introduction of a new cultivar will incur additional coststo the seed producer, the grower, processor and consumer; for specialadvertising and marketing, altered seed and commercial productionpractices, and new product utilization. The testing preceding release ofa new cultivar should take into consideration research and developmentcosts as well as technical superiority of the final cultivar. Forseed-propagated cultivars, it must be feasible to produce seed easilyand economically.

Once the inbreds that give the best hybrid performance have beenidentified, the hybrid seed can be reproduced indefinitely as long asthe homogeneity of the inbred parent is maintained. A single-crosshybrid is produced when two inbred lines are crossed to produce the F₁progeny. A double-cross hybrid is produced from four inbred linescrossed in pairs (A×B and C×D) and then the two F₁ hybrids are crossedagain (A×B)×(C×D). Much of the hybrid vigor exhibited by F₁ hybrids islost in the next generation (F₂). Consequently, seed from hybridvarieties is not used for planting stock.

Corn is an important and valuable field crop. Thus, a continuing goal ofplant breeders is to develop stable, high yielding corn hybrids that areagronomically sound. The reasons for this goal are obviously to maximizethe amount of grain produced on the land used and to supply food forboth animals and humans. To accomplish this goal, the corn breeder mustselect and develop corn plants that have the traits that result insuperior parental lines for producing hybrids.

SUMMARY OF THE INVENTION

According to the invention, there is provided a novel inbred corn line,designated LH225. This invention thus relates to the seeds of inbredcorn line LH225, to the plants of inbred corn line LH225 and to methodsfor producing a corn plant produced by crossing the inbred line LH225with itself or another corn line. This invention further relates tohybrid corn seeds and plants produced by crossing the inbred line LH225with another corn line.

DEFINITIONS

In the description and tables which follow, a number of terms are used.In order to provide a clear and consistent understanding of thespecification and claims, including the scope to be given such terms,the following definitions are provided:

Predicted RM. This trait for a hybrid, predicted relative maturity (RM),is based on the harvest moisture of the grain. The relative maturityrating is based on a known set of checks and utilizes conventionalmaturity systems such as the Minnesota Relative Maturity Rating System.

MN RM. This represents the Minnesota Relative Maturity Rating (MN RM)for the hybrid and is based on the harvest moisture of the grainrelative to a standard set of checks of previously determined MN RMrating. Regression analysis is used to compute this rating.

Yield (Bushels/Acre). The yield in bushels/acre is the actual yield ofthe grain at harvest adjusted to 15.5% moisture.

Moisture. The moisture is the actual percentage moisture of the grain atharvest.

GDU Silk. The GDU silk (=heat unit silk) is the number of growing degreeunits (GDU) or heat units required for an inbred line or hybrid to reachsilk emergence from the time of planting. Growing degree units arecalculated by the Barger Method, where the heat units for a 24-hourperiod are: ##EQU1## The highest maximum used is 86° F. and the lowestminimum used is 50° F. For each hybrid, it takes a certain number ofGDUs to reach various stages of plant development. GDUs are a way ofmeasuring plant maturity.

Stalk Lodging. This is the percentage of plants that stalk lodge, i.e.,stalk breakage, as measured by either natural lodging or pushing thestalks determining the percentage of plants that break off below theear. This is a relative rating of a hybrid to other hybrids forstandability.

Root Lodging. The root lodging is the percentage of plants that rootlodge; i.e., those that lean from the vertical axis at an approximate30° angle or greater would be counted as root lodged.

Plant Height. This is a measure of the height of the hybrid from theground to the tip of the tassel, and is measured in centimeters.

Ear Height. The ear height is a measure from the ground to the ear nodeattachment, and is measured in centimeters.

Dropped Ears. This is a measure of the number of dropped ears per plot,and represents the percentage of plants that dropped an ear prior toharvest.

DETAILED DESCRIPTION OF THE INVENTION

Inbred corn line LH225 is a yellow dent corn with superiorcharacteristics, and provides an excellent parental line in crosses forproducing first generation (F₁) hybrid corn.

Inbred corn line LH225 was developed from the single cross CM105×B37 byselfing and using an ear-row pedigree method of breeding. Selfing andselection were practiced within the above F₁ cross for seven generationsin the development of LH225. Some of the criteria used to select ears invarious generations include: yield, stalk quality, root quality, diseasetolerance, late plant greenness, late season plant intactness, earretention, pollen shedding ability, silking ability, and corn borertolerance. During the development of the line, crosses were made toinbred testers for the purpose of estimating the line's general andspecific combining ability, and evaluations were run by the Stanton,Minnesota Research Station. The inbred was evaluated further as a lineand in numerous crosses by the Stanton and other research stationsacross the Corn Belt. The inbred has proven to have a very goodcombining ability in hybrid combinations.

The inbred has shown uniformity and stability for all traits, asdescribed in the following variety description information. It has beenself-pollinated and ear-rowed a sufficient number of generations, withcareful attention to uniformity of plant type to ensure homozygosity andphenotypic stability. The line has been increased both by hand andsibbed in isolated fields with continued observation for uniformity. Novariant traits have been observed or are expected in LH225.

Inbred corn line LH225 has the following morphologic and othercharacteristics (based primarily on data collected at Williamsburg,Iowa):

VARIETY DESCRIPTION INFORMATION

A. Maturity

INBRED=LH225

Best Adapted For: Northcentral Regions of the Corn Belt

Heat Unit Silk: 1360 ##EQU2## B. Plant Characteristics

Plant height (to tassel tip): 199 cm.

Length of top ear internode: 14 cm.

Number of tillers: None

Cytoplasm type: Normal

Ear height (to base of top ear): 71 cm.

Number of ears per stalk: Single

C. Leaf

Color: 5 GY 3/4 Munsell Color Charts for Plant Tissues

Angle from stalk: <30°

Marginal waves: Many

Width (widest point of ear node lead: 10 cm.

Number of leaves (mature plants): 13

Sheath pubescence: Heavy

Longitudinal creases: Few

Length (ear node leaf): 68 cm.

D. Tassel

Number of lateral branches: 4

Branch angle from central spike: 30°-40°

Pollen shed: Medium

Anther color: Dark Purple

Glume color: Green with brown margin

Peduncle length (top leaf to basal branch): 9 cm.

E. Ear (Husked Ear Data Except When Stated Otherwise)

Length: 15 cm.

Midpoint diameter: 38 mm.

Weight: 71 gm.

Kernel Rows: Distinct, Straight

Number of Kernel rows: 14

Silk color: Green

Husk color (fresh): Light green

Husk color (dry): Buff

Husk extension: Long

Shank length: 12 cm.

Shank (no. of internodes): 8

Taper of Ear: Average

Husk leaf: <8 cm.

Position of shank (dry husks): Upright

F. Kernel (Dried)

Size (from ear midpoint)

Length: 12 mm.

Width: 8 mm.

Thickness: 4 min.

Shape grade (% rounds): >80

Pericarp color: Variegated: bronze at the pedicel becoming colorless atthe crown

Aleurone color: White

Endosperm color: Yellow

Endosperm type: Normal starch

Gm Weight/100 seeds (unsized): 24 gm.

G. Cob

Diameter at midpoint: 30 mm.

Strength: Strong

Color: Red

This invention is also directed to methods for producing a corn plant bycrossing a first parent corn plant with a second parent corn plant,wherein the first or second corn plant is the inbred corn plant from theline LH225. Further, both first and second parent corn plants may befrom the inbred line LH225. Therefore, any methods using the inbred cornline LH225 are part of this invention: selfing, backcrosses, hybridbreeding, and crosses to populations. Any plants produced using inbredcorn line LH225 as a parent are within the scope of this invention.Advantageously, the inbred corn line is used in crosses with other cornvarieties to produce first generation (F₁) corn hybrid seed and plantswith superior characteristics.

As used herein, the term "plant" includes plant cells, plantprotoplasts, plant cell of tissue culture from which corn plants can beregenerated, plant calli, plant clumps, and plant cells that are intactin plants or parts of plants, such as pollen, flowers, kernels, ears,cobs, leaves, husks, stalks, and the like.

Tissue culture of corn is described in European Patent Application,Publication No. 160,390, incorporated herein by reference. Corn tissueculture procedures are also described in Green and Rhodes, "PlantRegeneration in Tissue Culture of Maize", Maize for Biological Research(Plant Molecular Biology Association, Charlottesville, Va. 1982), at367-372. Thus, another aspect of this invention is to provide for cellswhich upon growth and differentiation produce the inbred line LH225.

The closest related art to LH225 is the corn line LH146. As a line LH225has specific combining ability with LH82 and possibly LH82 derivatives.When in combination with LH82, LH225 has very rapid dry down. This isunexpected due to the lateness of B37 which theoretically makes up onehalf of LH225's genetic makeup. B37 is a line that historically was usedin the extreme Southern corn growing areas and the South Central corngrowing areas (e.g. Southeastern United States, Southern Indiana,Southern Ohio, etc.). LH225 is adapted to the more Northern corn growingareas.

Table 1 shows the interpretation of disease ratings and Table 2 showshead to head comparisons of LH225 versus LH146 in hybrid combinations.Column 2 of Table 1 indicates the pedigrees tested and column 4 showsthe total number of geographical locations where these pedigrees werecompared. Column 5 (#1 Hybrid Mean) shows the mean values of the firstgenotype listed in column 2. Column 6 indicates the trait orcharacteristics (Yield, Moisture, Stalk Lodging and Root Lodging).Column 7 shows the difference between the first genotype listed incolumn 2 versus the second genotype (Genotype #1 minus Genotype #2).Column 8 shows the statistical probability and column 9 indicatesgeneral notes on the comparison.

                  TABLE 1                                                         ______________________________________                                        INTERPRETATION OF DISEASE RATINGS                                             Rating                                                                        ______________________________________                                        0 =     0% of the plant showing lesions                                       1 =     Less than 5% of the plant covered with lesions                        2 =     Less than 10% of the plant covered with lesions                       3 =     Less than 30% of the plant covered with lesions                       4 =     Less than 40% of the plant covered with lesions                       5 =     Less than 50% of the plant covered with lesions                       6 =     Less than 60% of the plant covered with lesions                       7 =     Less than 70% of the plant covered with lesions                       8 =     Less than 80% of the plant covered with lesions                       9 =     80-100% of the plant covered with lesions                             ______________________________________                                    

                                      TABLE 2                                     __________________________________________________________________________    LH225 - Head to Head Comparisons                                              Comparison                                                                           Pedigrees      #1 Hybrid                                               No.    Compared Year                                                                             Loc.                                                                             Mean  Trait                                                                             Diff.                                                                              Prob.                                                                             Notes                                __________________________________________________________________________    1      LH225 × LH82                                                                     1991                                                                             17 177.65                                                                              Yield                                                                             +22.647                                                                            .000                                            LH146 × LH82                                                                        17 18.09 Mst +0.729                                                                             .026                                                        17 5.47  Stalk                                                                             +0.882                                                                             .484                                                        16 0.19  Root                                                                              +0.063                                                                             .333                                     2      LH225 × LH82                                                                     1992                                                                             57 178.53                                                                              Yield                                                                             +18.877                                                                            .000                                            LH146 × LH82                                                                        57 22.95 Mst +0.422                                                                             .028                                                        57 5.46  Stalk                                                                             +0.596                                                                             .363                                                        57 0.93  Root                                                                              -0.596                                                                             .198                                     3      LH225 × LH165                                                                    1992                                                                             15 168.47                                                                              Yield                                                                             +7.133                                                                             .038                                            LH146 × LH165                                                                       15 24.02 Mst +3.175                                                                             .000                                                        15 1.607 Stalk                                                                             -1.067                                                                             .340                                                        15 0.00  Root                                                                              -0.467                                                                             .131                                     4      LH225 × LH167                                                                    1992                                                                             11 171.64                                                                              Yield                                                                             +19.091                                                                            .004                                            LH146 × LH82                                                                        11 23.68 Mst +1.470                                                                             .012                                                        11 2.00  Stalk                                                                              0.000                                                                             1.00                                                        11 0.00  Root                                                                              -0.091                                                                             .341                                     5      LH225 × LH85                                                                     1992                                                                              8 165.13                                                                              Yield                                                                             -2.375                                                                             .446                                            LH146 × LH82                                                                         8 19.15 Mst -1.224                                                                             .074                                                         8 1.50  Stalk                                                                             -1.000                                                                             .316                                                         8 0.25  Root                                                                              +0.125                                                                             .351                                     6      LH225 × LH82                                                                     1991                                                                             16 177.81                                                                              Yield                                                                             +9.688                                                                             .047                                            P3751       16 17.98 Mst +0.383                                                                             .085                                                        16 5.38  Stalk                                                                             +0.750                                                                             .560                                                        15 0.20  Root                                                                              +0.067                                                                             .334                                     7      LH225 × LH82                                                                     1992                                                                             57 178.53                                                                              Yield                                                                             -2.158                                                                             .363                                     8      P3751       57 22.95 Mst -0.195                                                                             .378                                                        57 5.46  Stalk                                                                             +3.667                                                                             .000                                                        57 0.93  Root                                                                              -0.018                                                                             .948                                     __________________________________________________________________________

Comparison 1 and 2 compares LH225×LH82 versus LH146×LH82. LH146 ×LH82has been used extensively in the Northern corn growing areas such as NewYork and Minnesota. LH146 whose parentage includes CM105 and B73(three-fourths CM105 and one-fourth B73) is a line that has realizedlarge usage in these Northern corn growing areas. LH146 is the closestcommercially used line to the new invention LH225. In each of two years,the hybrid LH225×LH82 had a highly significant yield advantage to thecommercial hybrid LH146×LH82 (22 bushels/acre in 1991 and 19bushels/acre in 1992). The grain moisture was slightly higher (0.7% and0.4% in 1991 and 1992 respectively), but this is much lower than a plantbreeder would anticipate given the parentage of LH225. Further, thismoisture disadvantage is not substantial when consideration is given tothe magnitude of the yield advantages.

Comparison 3 compares LH225 with LH146 in another cross involving anLH82 derivative which is LH165. The parents of LH165 are LH82 and LH51.LH225 again contributed a significant yield advantage over LH146 in thehybrid combination. In this case, however, there was substantially moregrain moisture associated with the LH225×LH165 cross. Grain moisture anddry down are traits that are complexly inherited and unpredictable.Compared to the line LH146, LH225 contributed to higher moisture whencrossed to LH165. The relative magnitude of this moisture difference andthat which was demonstrated with LH82 (comparison 1 and 2) issurprising. These two hybrids (comparison 1, 2, and 3) demonstrate quitedifferent patterns for grain moisture dry down between LH225 and LH 146.

The remaining comparisons (comparisons 4, 5, 6, and 7) show theperformance of LH225 in hybrid combinations compared to competitivehybrids that are used in the same areas to which the LH225 crosses areadapted. LH225×LH167 compared to LH146×LH82 (comparison 4), hadsignificantly and substantially higher yield (19 bushels/acre) and moremoisture. LH225×LH85 compared to LH146×LH82 (comparison 5) had equalyield, but in this case significant and substantially lower grainmoisture. In comparisons 6 and 7, LH225×LH82 is compared to the verywidely grown hybrid Pioneer Brand 3751 in both 1991 and 1992. In 1991,LH225×LH82 had significantly higher yield than 375 1 and equal grainmoisture. In 1992, yield and moisture were the same but LH225×LH82 hadsomewhat more stalk lodging. LH225×LH82 is phenotypically very diversefrom the hybrid Pioneer brand 3751 (genetic diversity is assumed by abreeder skilled in the art but the exact parentage of 3751 has not beenpublically disclosed). In each of these comparisons (comparisons 4, 5,6, and 7), the LH225 cross had value beyond that of the competitivehybrid 3751 for yield, grain dryness, and genetic diversity.

DEPOSIT INFORMATION

Inbred seeds of LH225 have been placed on deposit with the American TypeCulture Collection (ATCC), Rockville, Md. 20852, under Deposit AccessionNumber 75565 on Oct. 6, 1993. A Plant Variety Protection Certificate isbeing applied for with the United States Department of Agriculture.

Although the foregoing invention has been described in some detail byway of illustration and example for purposes of clarity andunderstanding, it will be obvious that certain changes and modificationsmay be practiced within the scope of the invention, as limited only bythe scope of the appended claims.

What is claimed is:
 1. A method for producing first generation (F₁)hybrid corn seed, said seed being capable of producing a hybrid cornplant having the characteristics of wide leaves, robust plant type, andconsistent and superior hybrid grain yield and dry down when compared toelite hybrids used in the northern corn region, comprising crossing afirst inbred parent corn plant with a second inbred parent corn plantand harvesting the resultant first generation (F₁) hybrid corn seed,wherein said first or second parent corn plant is the corn plant ofLH225, the seed of which have been deposited and have ATCC Accession No.75565.
 2. The method of claim 1 wherein the corn plant LH225, the seedof which have been deposited and have ATCC Accession No. 75565, is thefemale parent.
 3. The method of claim 1 wherein the corn plant LH225,the seed of which have been deposited and have ATCC Accession No. 75565,is the male parent.
 4. A first generation (F₁) hybrid corn plantproduced by growing said hybrid corn seed of claim 1.